I've found it much easier and I get better results using Google's site search. You just use Google's regular search box, only type in site:
http://bikeforums.net then whatever search term you are looking for. So if you want to search for "long Haul Trucker", You would type in "site:
http://bikeforums.net long haul trucker" No quotation marks. You can do this for any site. Try it, I think you will like it.